Fluidized bed reactors and moving bed reactors are examples of reactors where catalyst particles within the reactor are in motion during operation of the reactor. Based on the movement of the catalyst, it is possible to withdraw catalyst from a reactor during operation. This can allow for replacement and/or regeneration of catalyst. Unfortunately, the movement of catalyst within a reactor can lead to catalyst attrition due to collisions of catalyst particles with other catalyst particles and/or surfaces within a reactor. In addition to causing increased catalyst replacement costs, attrition of catalyst particles can potentially allow catalyst fragments and/or catalyst particles of reduced size to become entrained in the product effluent, with the result that catalyst fragments and/or reduced size particles may travel to unintended portions of a reaction system.
Some types of systems for controlling solid particle transport within a reaction system can include an “L”-valve. U.S. Pat. Nos. 4,685,482 and 4,687,382 describe examples of L-valve systems for controlling particle transport. One difficulty with L-valve systems is that a dead zone for catalyst particles can occur at the 90° angle in the L-valve flow path. Other difficulties can be related to the required fluid flow for the L-valve to operate. In situations where catalyst particles are separated from the liquid product effluent prior to passing through the L-valve, an additional gas flow can be required to induce movement of the catalyst particles through the L-valve. This can create difficulties in controlling the flow rate of the catalyst particles in situations where lower flow rates are desired.